Receiver mechanism for remote writing instrument



Nov? 1960 B. WEINGART EI'AL 2,959,637

RECEIVER MECHANISM FOR REMOTE WRITING INSTRUMENT INVENTORS F/G/ 3 xFiled Aug. 5, 1955 BEN WE/NGART JACK/7. Z/LLMA/V ROBERT E POOLE ATTORNEYUnited States Patent RECEIVER MECHANISM FOR REMOTE WRITING INSTRUMENTBen Weingart, 1301 Wilshire Blvd., Los Augeles, Jack Howard Zillman,Redondo Beach, and Robert Emmet Poole, Jr., La Habra, all of Calif.;said Zillman and said Poole assignors to said Ben Weingart Filed Aug. 5,1955, Ser. No. 526,752

4 Claims. (Cl. 178-18) This application is a continuation-in-part of ourcopending patent application Serial Number 496,306, filed March 23,1955, entitled Remote Writing Instrument and has for its general objectthe provision of an improved fluid damping mechanism for a remotewriting device of the general type there disclosed and claimed.

In the apparatus of the above-identified patent application the remotewriting instrument uses electrical signals to indicate the position ofthe two writing arms of the transmitter. These signals may, for example,be the stator voltage generated in a pair of selsyn or synchrogenerators which vary in magnitude and phase in accord with the writingmovements. In the receiver, cooperating motors, such as selsyn orsynchro motors, are connected to respond to the same stator voltages. Afollow-up or closed cycle control mechanism responds to the resultantinduced rotor voltage in each selsyn or synchro to energize power drivemeans on the receiver to rotate the respective receiver arms indirection and amount to bring these arms to correspondence with thetransmitted signals and hence with the positions of the transmitterarms.

Since the mechanism uses a follow-up system which is in essence a closedcycle control system, problems of hunting and instability arenecessarily encountered. Moreover, these problems become more acute asthe frictional and inertia resistance to writing arm movement increasesand as increased amplification is embodied in the system. This huntingand instability problem is troublesome for a number of reasons. It maygive rise to flutter or waving pen movement when a straight line isdrawn, to the annoyance of the user. It may give rise to loss of writingresponse, especially at high speeds, so that readability is impaired andthe chance of error increased. It may make the system critical as toexternal conditions of vibration, temperature, etc. For these and otherreasons it is highly desirable to provide in the system itself a meansto minimize hunting and instability.

In accordance with the present invention hunting and instability in theremote writing system is reduced or prevented by use of each writing armdrive motor itself as a mechanical damping device. This is accomplishedby providing a silicone oil filling in each motor, so that the motoritself experiences resistance to rotor movement substantiallyproportional to the rapidity of movement. The damping efiect thusprovided is effective at a point in the follow-up system where it ismost helpful in improving overall system operation and is in a form thatdoes not entail reduced amplification, on the one hand, or additionalmechanical or electrical damping apparatus, on the other. By a properselection of the oil viscosity the damping constant can be controlled toprovide a value capable of giving stable operation of the system withoutundesirable sluggish response.

In accordance with a further feature of the present invention thisdamping is effected with increased efficiency by providing a round rotorand stator motor construction. With this arrangement each motor definesa very small annular gap within which the damping fluid is located and ahighly eflicient nearly perfect viscous resistance to rotor movement.

It is therefore a general object of the present invention to provide areceiver for a remote writing system characterized by a high degree ofstability and lack of hunting and yet being of simple construction.

More specifically it is an object of the present invention to provide areceiver for a remote writing system wherein the writing arm drivemotors themselves serve to introduce damping into the system.

Still another object of the present invention is to provide a receiverfor a remote writing instrument wherein the receiver drive motors aremechanically arranged to provide effective damping.

Additionally, it is an object of the present invention to provide areceiver for a remote writing system which is characterized bysimplicity, ruggedness, reliability, small size, and low cost, allachieved with a high degree of stability and lack of tendency to hunt oroscillate.

The novel features which we believe to be characteristic of ourinvention are set forth with particularity in the appended claims. Ourinvention itself, however, together with further objects and advantagesthereof, will bestbe understood by reference to the followingdescription taken in conjunction with the accompanying drawings inwhich:

Figure l is a diagrammatic View showing a complete remote writingmechanism of the kind to which the receiver of the present invention isapplicable;

Figure 2 is a view in perspective of a receiver mechanism of the kind towhich the present application is applicable;

Figure 3 is a shematic circuit diagram showing one complete channel ofthe remote writing system;

Figure 4 is a view in axial cross-section with the rotor in elevation ofa receiver arm drive motor of the kind used in the system of the presentinvention;

Figure 5 is an enlarged cross-sectional view through axis 55, Figure 4;and

Figure 6 is a greatly enlarged fragmentary view of a portion of Figure 5showing how the windings are em bedded in the slots and the open facesof the slots arefilled with insulating material to define smoothcylindrical inner and outer faces.

The complete remote writing system to which the present invention isapplicable is described and claimed in our co-pending applicationentitled Remote Writing Instrument, Serial Number 496,306, filed March23, 1955 by the same applicants as the present invention and assigned tothe same assignee. The complete construction of the system is describedin that application in detail. For purposes of the present applicationit is sufficient to note that the system includes a transmitter 10,Figure 1, and a receiver 20. The transmitter includes a Writing device24 which is manually moved over a writing surface (not shown) to executeWriting motions. The writing device is connected to the arms 32 and 28of the transmitting selsyns or synchros 36 and 34, respectively, by thelinks 30 and 26. Arms 32 and 28 are pivotally connected to the links 30and 26, respectively. Thus as writing proceeds the arms 32 and 28 swingin accordance with writing motions, the position of rotation of the arms32 and 28 at any instant defining the position of the writing device 24.

In the receiver 20 a writing device 54, such as a ball point pen, isprovided to trace the same writing movements as the writing device 24.The device 54 is linked by links 56 and 58 to the arms 60 and 62 whichare rotated by the motors 64 and 66. As hereinafter described, thesemotors may conveniently be two-phase induction motors each of which isdriven in unison with the arms 32 and 28 of the transmitter 10. Theresultant motion of arms 60 and 62 drives the pen 54 in the desiredwriting movements which constitute the same writing movements as thoseexecuted by the writing device 24.

A pair of selsyn or synchro receivers 170 and 70, Figure l, aremechanically attached to the motors 64 and 66, respectively, to rotatein unison therewith. These receiving selsyns each are connected to thecorresponding transmitter selsyn 36 or 34. Hence the electricalenergization of the stator windings of the selsyns or synchros 17 and 70produces a magnetic field in each which is oriented in accordance withthe orientation of the rotors of the selsyns 36 and 34, respectively.The rotor windings of the selsyns 170 and 70 are connected to amplifiers168 and 68, respectively, to supply power to the motors 64 and 66. Thispower is of magnitude and sense to drive the motors 64 and 66 indirection to bring the arms 60 and 62 to positions corresponding withthose of arms 32 and 28 and thereby tend to reduce to zero the voltagesinduced in the rotors of selsyns 70 and 170.

The complete electrical circuit of one channel of the above describedsystem is shown in Figure 3. In this figure, the rotor Me of the selsyn34 is mechanically rotated by the arm 28 (Figure 1) and receivesalternating voltage from the source 72. The three stator windings of theselsyn 34 thereupon produce voltage across the terminals 340 in accordwith the position of the rotor. This voltage is communicated through theconductors 34 to the stator Winding terminals 700 of the similar statorwinding on the receiving selsyn 70. The latter generates a magneticfield of orientation corresponding to the orientation of the rotorwinding 34a of the transmitting selsyn 34. The rotor winding 70a of thereceiving selsyn 70 has induced in it a voltage determined by the extentand direction its position of rotation departs from the position for noinduced voltage at the particular current flows in the stator windingsof that selsyn. This voltage is of the same frequency as source 72 (i.e.60 cycles) and is amplified by amplifier 68 and applied to thequadrature winding 660 of the two-phase induction motor 66. Thereference phase winding 66d of this motor is applied through the phaseshifting capacitor 78 from source 72, which as above described furnishesthe voltage for the rotor winding 342 of the transmitting selsyn 34. Theresultant current flows in windings 66c and 66d create torque in therotor 66b of the motor 66, torque determined by the magnitude andrelative phase positions of the currents. The entire system is soconstructed that this torque is in direction to restore the rotor 70a ofthe receiving selsyn 70 to the position of no-induced voltage.

It will thus be seen that the complete system of the receiver, includingselsyn 70, amplifier 68 and motor 66, serves as a follow-up or closedcycle control system to bring the rotor of selsyn 70 to a positioncorresponding with that of the rotor of selsyn 34.

Figure 2 shows a perspective view of the receiving instrument of thekind to which the present invention is applicable. The drive motors 64and 66 straddle the writing surface formed by the backing plate 50 and aserrated edge 50a across which the paper 44a may be torn. The paper istaken from the roll 44 supported by angle brackets '42 which are mountedon the base plate 40, the shaft 43 serving to hold the roll 44 inposition. The pen 54 is pivotally connected to the links 56 and 58, eachof which is pivot-able at 57 and 59 in arms 60 and 62, respectively. toprovide a mechanical linkage essentially like that of the transmitter.The arms 60 and 62 are mounted -'on the shafts 64a and 66a of the motors64 and 66, respection of the drive motor 66. As shown, the squirrel cagerotor 66b has a plurality of skewed peripheral slots 66k, each of whichreceives a conductor of aluminum or similar material. This is preferablyaccomplished by flowing molten aluminum into the assembled rotorlaminations and then machining the rotor face to a smooth cylindricalconfiguration, all as is well understood in the induction motor art.

The stator 66e of the motor 66 has a plurality of sequentially shapedslots within which the windings 66c and 66d are disposed as shown. Thesewindings are totally enclosed by the magnetic parts of the structurewith the exception of the slots 66f located between each sequential slotand the inner periphery of the rotor. Each slot 66 is filled with anon-magnetic plastic material as is hereinafter described.

In order to provide a maximum degree of magnetic efliciency, the air gap66g, formed between the rotor 66b and the stator 66e, is made as shortas possible. In practical motors of the kind used in the apparatus ofthe present invention the diameter of the rotor 66a might be about /2inch and the air gap 66g might be about .0015 inch.

The motor 66 is encased at one end by the cap 67. This cap snugly fitsover the stator of the motor and defines a fluid seal in conjunctionwith the gasket 67a. Additionally there is provided an insulating member67b in the cap 67 and a series of conductor pins 67c embedded therein topermit motor circuit connections without losing the fluid seal of space6701'. The bearing 66h is of a type, such as an unsealed ball hearing,which does not close the passage from the space 67d to the gap 66g ofthe motor. However the opposite bearing 66f either serves to effect aseal or gasket means (not shown) is provided to prevent the escape ofsilicone oil from the gap 66g.

The cavity 67d and the gap 66g are flooded with silicone oil. Thisprovides a complete oil film of thin cylindrical conformation betweenthe rotor 66b and the inner periphery of the stator. This innerperiphery is of smooth cylindrical conformation and is preferably madein such conformation by flooding the stator, after winding, with aplastic material; allowing the plastic to harden; and then machining theinterior surface of the stator to a smooth cylindrical conformation ofthe requisite diameter.

Since the follow-up or servo system defines a closed circuit amplifyingsystem, it has a natural tendency toward hunting and instability. Thisis inherent in the system itself. 'In an apparatus of the kind to whichthe present invention is applicable the tendency towards hunting andinstability is marked. This is in part because of the very considerableinertia of the outwardly extending arms 60 and 62, together with thelinks 56 and 58 and the pen 54. It is also due to the necessity ofproviding a large amphfication in the amplifier 68, with a comparativelysmall voltage induced in winding 70a, Figure 3, giving rise to acomparatively great current flow in winding 660 in response to acomparatively small deviation in the position of rotor 70a from the novoltage position. For these reasons the pen 54, Figure 2, has a tendencyto form a wavy line and to overshoot or otherwise distort the writingaction during rapid writing.

In accordance with the present invention the stability of the system isgreatly enhanced by providing a fluid damping effect in the motors 64and 66. This is accomplished by flooding the motors with a silicone oil,consisting of an oily organo-silicon compound. Such oils arecharacterized by highly uniform viscosity characteristics over a rangeof temperatures and by inertness to the plastic material used in themotors. Thevery minute gap provided between the rotor and stator in themotors serves to provide a very thin film of the oil across which thefluid shearing or viscous action takes place. As a consequence themotors when flooded with the silicone oil serve to generate an increasedcounter force on the motors as the velocityof shaft rotation increases.

In an actual system it has been found that the viscosity of the siliconeoil should be about 500 centistokes for best results. Larger viscosityoils, such as 1000 centistoke oils can be used but tend to make thesystem sluggish. Oils of lesser viscosity tend to encourage instabilityand hunt.

It has been found that the damping obtained by the flooding of thereceiving motor is highly etfective in imparting stability to thefollow-up system. This is believed to be due to several effects. One ofthese is the very high damping constant that can be obtained with thevery narrow air gap involved, coupled with the smooth inner and outersurfaces of the rotor and stator of the motors. This results from thefact that the rotor and stator surfaces are very close together, givingonly a minute film across which fluid shearing takes place.Additionally, the damping action is at an efiective point in the closedcycle control system as it is directly operative on the motors 64 and 66and is thus effective on the output side of the unit.

Additionally, the mechanism is especially effective because it isunnecessary to provide additional apparatus for damping purposes. Thesynchro or selsyn, the motor, and the amplifier are all as designedentirely apart from the damping. The damping efiect is obtained merelyby placing the necessary silicone oil in position to flood the motors 64and 66. As the motors are sealed in any event, it is a simple matter toflood them with the oil. This is unlike the damping that could beachieved by ordinary means, such as a magnetic brake and eddy currentbrake, dashpot, or similar apparatus, which not only must be added tothe system but inherently increases the inertiaand such increasedinertia necessarily makes the system more susceptible to instability andcompels the use of a sluggish overall control system.

Because of the highly efiective damping provided by the presentinvention it is not necessary to provide feedback in the amplifier 68.Without the damping such feedback was found necessary to reduce the timedelay in the amplifier to a value not giving undue hunting orinstability.

While we have shown and described a specific embodiment of the presentinvention, it will, of course be understood that various modificationsand alternative constructions may be made without departing from thetrue spirit and scope thereof. We therefore intend by the appendedclaims to cover all such modifications and alternative constructionsfalling within their true spirit and scope.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a drive mechanism for a remote writing instrument having a writingarm driven by a servo system including a motor having a stator memberand an armature member with a space therebetween and with one of saidmembers being fixed and the other member being rotatable with respectthereto and being connected to said arm, said system and arm beingsubject to hunting and flutter which impair the readability of thewriting, the improve ment comprising: fluid seal means at each end ofsaid members to provide a fluid tight seal between said members at eachend of said space; and a liquid dampening medium in said space betweensaid members; whereby the liquid provides a viscous dampening of themovement of the movable member and writing arm to ameliorate the huntingand flutter of the arm.

2. In a drive mechanism for a remote writing instrument having a writingarm driven by a servo system including a motor having a stator memberand an armature member with a space therebetween and with one of saidmembers being fixed and the other member being rotatable with respectthereto and being connected to said arm, said system and arm beingsubject to hunting and flutter which impair the readability of thewriting, the improvement comprising: fluid seal means at each end ofsaid members to provide a fluid tight seal between said members at eachend of said space; and an oil of relatively uniform viscositycharacteristics in said space between said members as a dampeningmedium; whereby the oil provides a viscous dampening of the movement ofthe movable member and writing arm to ameliorate the hunting and flutterof the arm.

3. In a drive mechanism for a remote writing instrument having a writingarm driven by a servo system including a motor having a stator memberand an armature member with a space therebetween and with one of saidmembers being fixed and the other member being rotatable with respectthereto and being connected to said arm, said system and arm beingsubject to hunting and flutter which impair the readability of thewriting, the improvement comprising: fluid seal means at each end ofsaid members to provide a fluid tight seal between said members at eachend of said space; and a silicone oil having a viscosity of about 500centistokes in said space between said member as a dampening medium;whereby the oil provides a viscous dampening of the movement of themovable member and writing arm to ameliorate the hunting and flutter ofthe arm.

4. In a drive mechanism for a remote writing instrument having a writingarm driven by a servo system including a motor having a stator memberand an armature member with a space therebetween and with one of saidmembers being fixed and the other member being rotatable with respectthereto and being connected to said arm, said system and arm beingsubject to hunting and flutter which impair the readability of thewriting, the improvement comprising: providing a relatively smoothsurface on the portions of said members defining said space; saidmembers being so proportioned that the width of said space between themembers is very small; fluid seal means at each end of said members toprovide a fluid tight seal between said members at each end of saidspace; and a liquid dampening medium in said space between said members;whereby the liquid provides a viscous dampening of the movement of themovable member and writing arm to ameliorate the hunting and flutter ofthe arm.

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